PROJECTSUMMARY Thelong-termgoalofourresearchistounderstandthemolecularmechanismsthatcontroleukaryoticsignaling pathways. The objective of this application is to elucidate the principles that regulate the core kinases in the Hippopathway.TheHippopathwaycontrolsorgansizeduringdevelopment,tumorigenesis,andmaintainsthe stem-cell niche through the coordinated activity of a kinase cassette that includes two kinases, Mst1/2 and Lats1/2, and two accessory proteins, Mob1 and hSalvador. In Aim 1, we will establish a molecular basis for understandingcomplexformationbetweenSARAHdomainproteins(hSalvador,Mst1/2,andRassF5)toinform onhowtheseproteinsregulatepathwayactivity.InAim2,ourinvestigationswillfurtherunderstandingofMst1/2 activationandprovideamechanisticlinkbetweenupstreampathwaycomponentsandkinaseactivation.InAim 3wewillelucidatethemolecularmechanismsgoverningtheactivityofLats1andMst2activity.Outcomesfrom the proposed work will fundamentally alter our picture of Hippo signaling in normal and disease states and stimulatenewdirectionsofcellularandtherapeuticinvestigation.